Two employees of a general store were killed in an explosion after they were asked to go back inside Japan’s Aeon shopping mall that collapsed in the 6.8-earthquake, an official from the store said.

Executives of the company Habita have apologised to the families of the victims.

One of the victims was identified as 22-year-old Kurumi Otake, while the identity of the other was not made public.

Company sales manager Goji Yuse said the company instructed the two to put sales proceeds into the safe if it was possible. "The instructions given at the time were inappropriate, and I truly regret them," the manager said, according to reports in Japanese media.

He said the company was considering how to proceed with the matter. "Looking back now, it was not worth a life," Mr Yuse told reporters.

Otake's tearful mother reportedly told them: "I wish someone had stopped her."

"My daughter is not coming back."

The mall's operator said it believes the explosion was due to a gas leak and occurred after about 3,000 shoppers had been evacuated to a parking lot following the quake, but some employees remained inside.

Prime minister Sanae Takaichi visited earthquake-affected Kumamoto prefecture for the first time since the southwestern prefecture, leaving at least 38 people dead.

Ms Takaichi flew over affected areas from an army helicopter and visited one of the area's best-equipped shelters, with cardboard beds, partitions and air-conditioning, triggering criticisms on social media that her visit distorted reality.

The powerful earthquake and nearly 100 subsequent aftershocks, which struck Kumamoto last Tuesday, flattened homes, snapped bridges, crumbled roads and triggered an explosion at a shopping mall, sparking a massive search-and-rescue operation.

At least 38 people died in the quake and its aftermath, including one person who died of apparent heat stroke while taking shelter in a car in hot weather and one other whose cause of death is still being investigated.

More than 1,500 buildings were damaged, including 179 that were destroyed, according to preliminary assessments by Kumamoto officials.

Kumamoto governor Takashi Kimura, during his meeting with Ms Takaichi, said that the "abnormal heat" has been pounding on the already difficult lives of the residents.

Locals this week began clearing heaps of debris and putting out broken furniture and damaged appliances for collection, while in the towns of Uki and Hikawa, construction of temporary housing began.

Mr Kimura sought further government support to improve the living conditions at evacuation centers, saying many of them lack clean water and medical care.

"While taking into consideration the governor's requests, we will quickly examine what the government can do for the disaster-hit region and affected people and move proactively," Ms Takaichi said.

The complex had some 3,000 shoppers and hundreds of members of staff inside when the earthquake struck. About an hour later an explosion ripped through a part of the mall where some staff members were working, causing the second floor to collapse.

Rescuers pulled 12 people out of the mall with seven confirmed dead and five others injured.